Method of obtaining ductile beryllium

ABSTRACT

A critical relationship is described between the rate of cooling of beryllium from a stress-relieving or forming temperature and the indigenous iron-to-aluminum impurity ratio in mechanically worked beryllium, with resulting improvement in its ultimate ductility.

United States Patent 1191 Taylor et al.

1451 Feb. 12, 1974 METHOD OF OBTAINING DUCTILE BERYLLIUM Inventors: William Taylor, Wyomissing;

William O. Frauson, Conyngham; Stanley Chinowsky, Reading, all of 21 Appl. No.: 127,972

3,349,597 10/1967 Gross, Jr 75/150 X 3,333,994 8/1967 Mallen et al.... 148/13 2,872,363 2/1959 Macherey 148/11.5

OTHER PUBLICATIONS Beryllium lngot Sheet, Technical Bulletin No. 2210, The Beryllium Corporation, Reading, Pa., 1965.

Primary Examiner-Richard 0. Dean Attorney, Agent, or Firm-Pennie, Edmonds, Morton, Taylor & Adams ABSTRACT [52] US. Cl. l48/ll.5 F, 75/150, 148/13 [57] 51 lt.Cl. ..C22fll E geld of Search 7 75/150 1 48/11 5 R 1 1 A cr1t1cal relationship 15 descnbed between the rate of 48/13 cooling of beryllium from a stress-relieving or forming temperature and the indigenous iron-to-aluminum im- [56] eferences Cited purity ratio in'mechanically worked beryllium, with UNITED STA N S resulting improvement in its ultimate ductility. 3,065,117 11/1962 Brown et a1. 148/13 2 Claims, 1 Drawing Figure O 100 E Q. 800 a. Z 600 40o AI, pp

PAIENIEB EB 12w 200 400 600 800 I000 I200 I400 I600 I800 2000 2200 ATTORNEYS '1 METHOD BIAI FIG DUCTILEPERYLUUM.

This invention relates to beryllium metal and, more particularly, to a method of producing mechanically worked beryllium in ductile form.

Beryllium can be mechanically worked, as by rolling, extrusion or forming. When these operations introduce internal stresses in the beryllium product the stress must be relieved by an annealing-type heat treatment. A forming or annealing temperature of at least about 1,300F., and preferably of about 1,370F., is used and heating at temperature is carried out generally for from 20 minutes to as much as 2 hours. Following this heating, the beryllium is allowed to cool slowly as in the annealing of other metals, and slow cooling is generally effected by allowing the metal product to remain in the heat-treatment furnace while the furnace is allowed to cool to close to ambient temperature, a cooling rate that generally is of the order to 50F. per hour. In the case of worked but previously ductile beryllium, it has been found that this type of annealing treatment frequently causes embrittlement of the beryllium to the extent that it exhibits virtually no elongation at its breaking point under tensile testing in a direction transverse to the working direction.

We have now discovered that the transverse embrittlement of mechanically worked but previously ductile consolidated beryllium occurs during forming or stress relieving by heat treatment when the ratio of iron to aluminum, both indigenous impurities in beryllium, ex-

ceeds a certain value with respect to the total amount of these two impurities, and further that embrittlement of such beryllium can be avoided by relatively fast cooling of the heat-annea1ed beryllium through a critical portion of its cooling temperature range. That is, we have developed an improvement in the forming or stress relieving by heat treatment of mechanically worked beryllium having a total indigenous iron plus aluminum purity content not substantially in excess of 0.3 percent by weight present in a ratio of iron to aluminum greater than that represented by the line AB in the FIGURE of the drawing. In this stress relieving, the worked beryllium is heated to a temperature of at least about 1,300F. and we have found that the pre-stress relief transverse ductility of the beryllium is at least be more readily understood from the following description taken in conjunction with the accompanying drawing in which The FIGURE is a graph showing a line of critical indigenous iron-to-aluminum impurity ratios for varying I 2 amounts of these impurities normally present in ductile consolidated beryllium.

Beryllium metal of commercial grade generally contains between about 700 to 2,000 ppm of iron and between about and 1,400 ppm of aluminum as indigenous impurities. The ratio of iron to aluminum may vary widely in the grade unless special procedures are used to control the ratio. In exploring the effects of var ious impurities on the ductility of stress-relieved specimens of beryllium which had been mechanically worked by extrusion, we discovered that the transverse ductility of the stress-relieved specimen was virtually destroyed when the iron:aluminum ratio for various amounts of iron and aluminum were higher than, i.e., to the right and below, the values represented by the line AB in the FIGURE. Conversely, the transverse' ductility remained unchanged during stress-relieving when the iron:aluminum ratio for various amounts of iron and aluminum were lower than, i.e., to the left and above, the values represented by the line AB in the FIGURE.

In further investigation of the cause or factors that influenced destruction of transverse ductility in the aforementioned specimens during stress-relieving specimens having a higher iron:aluminum ratio than that represented by line AB in the FIGURE, we discovered that the embrittlement occurred during a specific portion of the cooling operation, to wit, during the period that the specimens were passed through the range of approximately 800F. to approximately 500F. as they were being furnace cooled at a conventional fumacecooling rate of about 50F. per hour by turning off the source of furnace heat. By diminishing the time that the specimens were permitted to remain at a temperature within this range, we found that the transverse ductility of the stress-relieved specimens could be retained and sometimes increased. To do this, we found that the specimens should be cooled through the range of 800F. to 500F. at a rate at least as fast as that obtained by removing the specimens from the furnace at about 800F. and by allowing them to cool in the ambient atmospheric air, e.g., at a rate of at least about 1,000F. per hour, so that the specimens had passed through the critical cooling temperature range in about 20 minutes. Still more rapid cooling is possible by directing an air blast against the specimens during this temperature interval. After the specimens had been cooled to at least 500F., they could be continued to be cooled in air or they could be returned to a furnace at a temperature no higher than 500F. and allowed to cool with the furnace at a conventional furnace-cooling rate.

The influence of cooling rate after stress-relieving on slabs of beryllium extruded from ductile consolidated beryllium of the type described hereinbefore is shown by thedata in the following table:

TABLE I Fe ppm A1 ppm Fe/Al Ratio Stress-relieving Conditions U.T.S. (ksiXlO) Transverse 0.2% Transverse Y.S. (ksiXlO) Elongation l:

1860 590 3.1 None 42.8 34.9

2 hr. 1370F, S.C. 42.2 nil nil 2 hr. 1370F, F.C." 45.9 41.2

1570 10.5 None 52.7 45.1

2 hr. 1370F, S.C. 49.0 nil ml 2 hr. 1370F, F.C. 56.3 50.6

1390 8.2 None 48.8 42.0 0.5

2 hr. 1370F, S.C 44.6 nil nil 2 hr. 1370F, F.C. 48.1 40.9 0.8

TABLE I Continued Ft: ppm Al ppm Fe/Al Ratio Stress-relieving Conditions U.T.S. (ksiXlO-l Transverse 0.2% Transverse Y.S. (ksiXlO) Elongation I380 130 7.7 None 56.5 V 47.0 0.8 2 hr. l370"F, S.C. 59.9 nil nil 2 hr. |370F, F.C. 57.8 50.7 1.2

I240 400 3.l None 50.9 45.5 1.0 2 hr. l370F, S.C. 44.2 nil nil 17 hr. l370F, F.C. 50.5 45.1 1.0

Slow cool in furnace at 50F. per hour "Fast cool in ambient atmosphere The following table presents data that shows that in xces f 0.3% by weightpercent in a ratio of iron slow cooling does not have any significant detrimental 5 to aluminum greater than that represented by the line effect on the transverse ductility of similar slabs of ex- AB in the FIGURE of the drawing and the beryllium' truded beryllium where the only difference is an ironhaving been treated to a temperature above about :aluminum ratio lower than that represented by the line 800F., the improvement whichcomprises cooling the Ag in the RIQQRE; M m" WNW heated beryllium at least as rapidly as can be effected TABLE ll Fe ppm Al ppm Fe/Al Ratio Stress-relieving Conditions U.T.S., (ksiXlO) Elongation (ksiXlO) 690 420 1.65 None 42.6 35.6 0.9

2 hr. l370F, s.c.* 41.1 33.7 0.9

1300 820 1.58 None 49.8 43.7 0.6

2 hr. 1370F. 50* 47.0 42.8 0.5

I280 1020 1.25 None 53.3 43.7 0.7

2 hr. l370F, s.c.* 50.1 40.2 0.7

1580 1370 1.16 None 50.8 43.1 0.6

2 hr. 13701=, s.c.' 47.1 40.6 0.4

700 1290 0.55 None 48.9 40.8 0.7

2 hr. 1370F, s.c.* 48.0 39.5 0.8

1570 g 780 2.0 None 49.8 43.5 0.5

2 hr. 13701=, s.c.* 47.9 41.6 0.5

Slow cool in furnace at 50F. per hour by cooling in the ambient atmospheric air through the 40 cooling range of about 800F. to about 500F.

1. In the cooling of mechanically worked beryllium 2. The method according to claim 1 in which the which has been heated for the purpose of forming or heated beryllium is cooled at a rate of at least about stress-relieving, the beryllium having a total indigenous 1,000F. per hour through the cooling range of about iron plus aluminum impurity contentnot substantially 800F. to about 500F.

5 can.-. We--- 

2. The method according to claim 1 in which the heated beryllium is cooled at a rate of at least about 1,000*F. per hour through the cooling range of about 800*F. to about 500*F. 